Physico-chemical considerations of titanium as a biomaterial Tengvall, P. and I. Lundstrom (1992), Clin Mater 9(2): 115-34.Abstract: Physico-chemical properties of titanium are discussed. Special attention is paid to those of amorphous TiO 2 that contact tissues in vivo. In aqueous environments TiO 2. (aq) has low ion-formation tendency and low reactivity with macromolecules. This is accompanied by low toxicity. Titanium does not facilitate reactive oxygen radical generation during inflammatory conditions as observed in in-vitro experiments. The outermost layers of the oxide are in the Ti(IV) oxidation state, although using electron spin resonance (ESR) techniques, formation of Ti(III) is observed at atmospheric conditions. The impact of similarities between water and TiO 2 is speculated upon, and the physico-chemical properties of titanium are tentatively linked to some in-vivo consequences.

Physicochemical evaluation of silica-glass fiber reinforced polymers for prosthodontic applications Meric, G., J. E. Dahl, et al. (2005), Eur J Oral Sci 113(3): 258-64.Abstract: This investigation was designed to formulate silica-glass fiber reinforced polymeric materials. Fused silica-glass fibers were chosen for the study. They were heat-treated at various temperatures (500 degrees C, 800 degrees C and 1100 degrees C), silanized, sized and incorporated in two modified resin mixtures (A and B). The flexural properties in dry and wet conditions were tested and statistically analyzed, and the content of residual methyl methacrylate (MMA) monomer, dimensional changes with temperature, water sorption and solubility were determined. Woven fibers [36.9% (wt/wt)], heat-treated at 500 degrees C, gave the highest strength values for the polymeric composites (an ultimate transverse strength of 200 Mpa and a flexural modulus of 10 GPa) compared with the fibers heat-treated at other temperatures. There was no statistically significant difference in the measured flexural properties between resins A and B regarding fiber treatment and water storage time. These fiber composites had a small quantity of residual MMA content [0.37 +/- 0.007% (wt/wt)] and very low water solubility, indicating good biocompatibility. It was suggested that silica-glass fibers could be used for reinforcement as a result of their anticipated good qualities in aqueous environments, such as the oral environment.

Physicochemical model of alginate-poly-L-lysine microcapsules defined at the micrometric/nanometric scale using ATR-FTIR, XPS, and ToF-SIMS Tam, S. K., J. Dusseault, et al. (2005), Biomaterials 26(34): 6950-61.Abstract: Alginate-poly-L-lysine-alginate (APA) microcapsules are currently being investigated as a means to immuno-isolate transplanted cells, but their biocompatibility is limited. In this study, we verified the hypothesis that poly-L-lysine (PLL), which is immunogenic when unbound, is exposed at the APA microcapsule surface. To do so, we analysed the microcapsule membrane at the micrometric/nanometric scale using attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. The results indicate that PLL and alginate molecules interact within the membrane. PLL exists in considerable amounts near the surface, contributing to the majority of the carbon within the outermost 100 Angstroms of the membrane. PLL was also detected at the true surface (the outermost monolayer) of the microcapsules. The exposure of PLL does not appear to result from defects in the outer alginate coating. This physicochemical model of APA microcapsules could explain their immunogenicity and will play an important role in the optimization of the microcapsule design.

Physicochemical properties and bioactivity of fungal chitin and chitosan Wu, T., S. Zivanovic, et al. (2005), J Agric Food Chem 53(10): 3888-94.Abstract: Chitinous material was extracted from mycelia of Aspergillus niger and Mucor rouxii grown in yeast peptone dextrose broth for 15 and 21 days, respectively. The extracted material was characterized for purity, degree of acetylation, and crystallinity and tested for antibacterial and eliciting properties. The maximum glucosamine level determined in the mycelium of A. niger was 11.10% dw and in the mycelium of M. rouxii was 20.13% dw. On the basis of the stepwise extraction of freeze-dried mycelia, it appeared that M. rouxii mycelia contained both chitin and chitosan, whereas A. niger contained only chitin. The yields of crude chitin from A. niger and M. rouxii were 24.01 and 13.25%, respectively, and the yield of chitosan from M. rouxii was 12.49%. Significant amounts (7.42-39.81%) of glucan were associated with chitinous compounds from both species and could not be eliminated by the extraction method used. The degrees of acetylation were determined to be 76.53 and 50.07% for chitin from A. niger and M. rouxii, respectively, and 19.5% for M. rouxii chitosan. The crystallinity of fungal chitin and chitosan was estimated to be less intense than in corresponding materials from shrimp shells. The extracted chitin and chitosan in a concentration of 0.1% reduced Salmonella Typhimurium DT104 2576 counts by 0.5-1.5 logs during a 4 day incubation in tryptic soy broth at 25 degrees C. Furthermore, all tested chitinous materials from fungal sources significantly reduced lesions caused by Botrytis cinerea and Penicillium expansum in harvested apples.

Physico-chemical properties of silk fibroin membrane as a biomaterial Minoura, N., M. Tsukada, et al. (1990), Biomaterials 11(6): 430-4.Abstract: A water-insoluble silk fibroin membrane was prepared by immersing a silk fibroin membrane as cast in 50 vol% aqueous methanol solution for different periods of time at 25 degrees C. To use the membrane as a biomaterial, oxygen and water vapour permeability, transparency, mechanical property and enzymatic degradation behaviour in vitro of the membrane in the wet state were investigated. These physico-chemical properties changed according to the condition of the methanol treatment. The membrane had oxygen permeability, water vapour permeability, transparency and biodegradability.

Physico-chemical surface characterization of hyaluronic acid derivatives as a new class of biomaterials Barbucci, R., A. Magnani, et al. (1993), J Biomater Sci Polym Ed 4(3): 245-73.Abstract: Three hyaluronic acid derivatives with different types and/or percentages of esterification, were analyzed by means of static contact angle measurements, SEM, ESCA, ATR/FT-IR, WAXS, DSC and TGA. The physico-chemical characterization of the three different samples, in both dry and wet state, was provided in terms of surface and bulk properties. ESCA and infrared analyses showed that the surface composition of all samples differs from that of the bulk. The hydrophilic-hydrophobic character of the samples changed according to the chemical composition as shown by ESCA and contact angle measurements. Both infrared and contact angle measurements reveal that surface restructuring occurred upon hydration for all the samples and the greater the hydrophilic character of the sample, the greater and faster the restructuring phenomenon. A clear picture of the different types of chemical groups has been established at different depth for the three materials.

Physiological and cell biological aspects of perfusion culture technique employed to generate differentiated tissues for long term biomaterial testing and tissue engineering Minuth, W. W., K. Schumacher, et al. (2000), J Biomater Sci Polym Ed 11(5): 495-522.Abstract: Optimal results in biomaterial testing and tissue engineering under in vitro conditions can only be expected when the tissue generated resembles the original tissue as closely as possible. However, most of the presently used stagnant cell culture models do not produce the necessary degree of cellular differentiation, since important morphological, physiological, and biochemical characteristics disappear, while atypical features arise. To reach a high degree of cellular differentiation and to optimize the cellular environment, an advanced culture technology allowing the regulation of differentiation on different cellular levels was developed. By the use of tissue carriers, a variety of biomaterials or individually selected scaffolds could be tested for optimal tissue development. The tissue carriers are to be placed in perfusion culture containers, which are constantly supplied with fresh medium to avoid an accumulation of harmful metabolic products. The perfusion of medium creates a constant microenvironment with serum-containing or serum-free media. By this technique, tissues could be used for biomaterial or scaffold testing either in a proliferative or in a postmitotic phase, as is observed during natural development. The present paper summarizes technical developments, physiological parameters, cell biological reactions, and theoretical considerations for an optimal tissue development in the field of perfusion culture.

Physiological strains induce differentiation in human osteoblasts cultured on orthopaedic biomaterial Di Palma, F., M. Douet, et al. (2003), Biomaterials 24(18): 3139-51.Abstract: We have developed an in vitro mechanical stretching model of osteoblastic cells cultured on metallic biomaterials in order to study the effects of mechanical strain on osteointegration of orthopaedic implants. Titanium alloy discs coated with alumina or hydroxyapatite were used as substrates. Three Dynacell devices were especially designed to apply cyclic strains on rigid biomaterials. The regimen (600 mu epsilon strains, 0.25Hz) was defined on the basis of physiological data and estimated deformation on hip stem prostheses. The performances of these apparatus were reproducible and provided controlled deformations. Human osteosarcoma cell line MG-63, human osteoblasts obtained from primary cultures and ROS 17/2.8 rat osteosarcoma cells were used as cell models. Cell behaviour was assessed in terms of growth and alkaline phosphatase (ALP) activity by in situ assays for two regimens: 15-min deformations repeated three times a day to mimic rehabilitation exercises and 24-h continuous deformations. We demonstrated that continuous deformation did not affect the growth and ALP activity of MG-63 cells, in contrast with sequential deformations which had no effect on cell number, but which stimulated ALP activity after 5 days of stretching. This sequential regimen can also modify the behaviour of human bone-derived cells resulting in increased proliferation after 5 days and stimulation of ALP activity after 15 days. ROS 17/2.8 rat osteosarcoma cells submitted to sequential deformations responded faster than other cell lines by increasing their ALP activity only after 1 day of stretching. Like MG-63 cells, proliferation of the ROS 17/2.8 rat osteosarcoma cell line was not affected by sequential deformations. This study suggests that short, repeated deformations defined to mimic rehabilitation exercises recommended after prostheses implantation are more likely to exert beneficial effects on implanted bone than continuous strains.

Piezoelectric contrast materials for ultrasound imaging Towe, B. C. (2005), IEEE Trans Ultrason Ferroelectr Freq Control 52(9): 1483-8.Abstract: Piezoelectric ceramics and polymers can be used as a type of marker and contrast material for medical ultrasound imaging systems. High-frequency electrical signals are detected from surface electrodes when these materials are introduced into conducting media such as tissue and scanned by ultrasound imaging systems. Detected signals are applied to the imaging circuits of a modified ultrasound system such that they display a unique type of electrical image that shows the piezomaterial's polarization, shape, and position at arbitrarily high contrast compared to the conventional ultrasound acoustic image. The resulting piezoelectric image can be merged in real-time with conventional ultrasound acoustic imaging to form a composite image. This approach is of interest in the development of improved techniques for imaging medical devices that are implanted or otherwise introduced into the body.

Plasma- and chemical-induced graft polymerization on the surface of starch-based biomaterials aimed at improving cell adhesion and proliferation Elvira, C., F. Yi, et al. (2003), J Mater Sci Mater Med 14(2): 187-94.Abstract: Plasma and chemical induced graft polymerization of acrylic monomers on starch-based biomaterials has been performed with the aim to improve cell adhesion and proliferation on the surface of the polymers, in order to adequate their properties for bone tissue engineering scaffolding applications. Plasma and chemical surface activation was aimed to induce the polymerization of acrylic polar monomers being carried out by applying a radio frequency plasma and expose the samples to a mixture of Ar/O2, or by immersion in a H2O2/(NH4)2S2O8 solution with UV radiation, respectively. Both procedures were followed by the graft polymerization of the corresponding monomers. Polymer grafting was analyzed by Fourier transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) and by contact angle measurements. Properties such as mechanical performance, swelling degree, and degradation behavior, as well as bioactivity, have been studied and compared for the different activation methods. Finally, preliminary cell adhesion and proliferation tests were performed, using goat bone marrow cells, showing a remarkable improvement with respect to original non-surface modified starch-based biomaterials.

Plasma coagulation response to surfaces with nanoscale chemical heterogeneity Miller, R., Z. Guo, et al. (2006), Biomaterials 27(2): 208-15.Abstract: A mixed film bearing nanoscale domains of one chemical functionality surrounded by another chemical functionality is shown to prolong material-induced coagulation of whole human blood plasma. In comparison, surfaces with uniform silane chemistry or physical mixtures of control surfaces bearing two different, uniform silane chemistries are found to be much more efficient activators of plasma coagulation on a per-unit-area basis. Binary mixed films are deposited on glass substrates by the sequential adsorption of 0.0001% 3-aminopropyltriethoxysilane (APS) followed by 0.1% n-butyltrichlorosilane (BTS). Creation of APS islands in a sea of BTS is confirmed by atomic force microscopy in friction mode. Results suggest that some yet-to-be-determined interfacial phenomena, perhaps associated with protein adsorption near the interface, may be altered by this nanoscale spatially distributed chemical heterogeneity, causing a decrease in contact activation.

Plasma lithography--thin-film patterning of polymeric biomaterials by RF plasma polymerization I: Surface preparation and analysis Goessl, A., M. D. Garrison, et al. (2001), J Biomater Sci Polym Ed 12(7): 721-38.Abstract: Plasma lithography, combining plasma deposition with photolithography, is described as a versatile method to manufacture all-polymeric substrates with thin-film patterns for applications in biomedical engineering. Patterns of a hydrophobic fluorocarbon plasma polymer with feature sizes between 5 and 100 microm were deposited on a base substrate in a lift-off process: an intermediate tetraglyme plasma polymer layer provides non-fouling properties to the base substrate. Careful analysis of critical process parameters identified the narrow window of process conditions that led to the formation of functional surface patterns. High pattern fidelity, aspect ratios, and resolution of the patterns are demonstrated by atomic force microscopy. Electron spectroscopy for chemical analysis (ESCA) and secondary ion mass spectroscopy (SIMS) were used to characterize the surfaces, showing good retention of the original chemical structure of the pattern components throughout the process. SIMS imaging was used for specific chemical imaging of the components. Potential applications for the patterned polymer films, e.g., for studying cell behavior in vitro in dependence of shape and size of adhering cells, are discussed.

Plasma processing of biomaterials Piskin, E. (1992), J Biomater Sci Polym Ed 4(1): 45-60.Abstract: Surface properties of biomaterials can easily be modified by glow-discharge plasma processing for very diverse biomedical applications. Activated carbon granules can be coated with a very thin polymeric membrane by plasma polymerization to improve their blood compatibilities without changing their adsorption capabilities. The problems associated with the microporous polypropylene oxygenator membranes can be eliminated by coating with a nonporous thin polymeric film in a glow-discharge reactor. Cell attachment and growth on polystyrene microcarriers can significantly be increased by alkylamine plasma treatment. Physical and chemical properties of polyurethane biomaterials can be tailor-made by plasma modification.

Plasma protein adsorption pattern on characterized ceramic biomaterials Rosengren, A., E. Pavlovic, et al. (2002), Biomaterials 23(4): 1237-47.Abstract: The protein/biomaterial interactions of three biomaterials used in hard tissue surgery were studied in vitro. A dynamic flow system and two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) were used to investigate the adsorption of proteins from diluted human plasma on hydroxyapatite, alumina and zirconia, with regard to total protein binding capacity, relative binding capacity for specific proteins and flow-through and desorption patterns. The ceramics were characterized regarding physicochemical properties; namely, chemical composition by elementary analyses and specific surface, pore volume and pore size distribution using the BET-method and Hg-porosimetry. The materials were found to adsorb a surprisingly low amount of plasma proteins, leaving more than 70% of the surface free. The cellular response will therefore be highly affected by the physico-chemical properties of the material, in contrast to a surface fully covered with proteins. Regarding the adsorption of proteins, most proteins exhibited similar flow-through patterns on the three adsorbents. The exceptions with different flow-through patterns were apolipoprotein D (Apo D), apolipoprotein J (Apo J), complement factor C1s (C1s), complement factor C3 (C3), ceruloplasmin, fibrinogen, alpha1 B glycoprotein and alpha2 HS glycoprotein and serum retinal-binding protein (SRBP). The role of these proteins on acceptance or rejection of implants has to be investigated.

Plasma recalcification as a measure of contact phase activation and heparinization efficacy after contact with biomaterials Rhodes, N. P. and D. F. Williams (1994), Biomaterials 15(1): 35-7.Abstract: The rate of plasma clotting was measured in order to investigate two different processes. In both cases normal, pooled platelet-poor plasma was used as a substrate for measurement of clotting. The intrinsic coagulation pathway was studied by bringing a variety of biomaterials into contact with a plasma aliquot and observing the rate of clotting diminish by virtue of factor XII activation. The efficacy of heparinization was investigated by measuring the increase in clotting time of a plasma aliquot during biomaterial contact. In both cases, clotting time was measured turbidometrically. Marked differences in intrinsic pathway activation were observed between a variety of materials. There were clear differences between the materials and the negative and positive controls. The assay showed that heparinized materials could be distinguished from non-heparinized materials and a non-activated plasma control.

Plasma-induced grafted polymerization of acrylic acid and subsequent grafting of collagen onto polymer film as biomaterials Lee, S. D., G. H. Hsiue, et al. (1996), Biomaterials 17(16): 1599-608.Abstract: Polyacrylic acid (pAA) was introduced onto Ar-plasma treatment silicone rubber (SR) membrane surfaces by plasma-induced grafted polymerization. Collagen (type III) was also linked with the carboxylic group of pAA grafted onto the SR surface via a carbodiimine agent to obtain a secondary structure of SR. The SR surface properties were characterized by ATR-FTIR, ESCA, contact angle, and SEM. The biocompatibility of the SR surface was evaluated by a culture of cornea epithelial (CE) cells. Subsequently, 75-450 micrograms cm-2 of pAA were obtained on the SR surfaces under different reactive conditions; 3-12 micrograms cm-2 of collagen were linked on modified surfaces of SR. Moreover, ATR-FTIR and ESCA were utilized to confirm the proceedings of these reactions. The hydrophility of the modified SR was measured by a contact angle meter. The values of contact angle for SR grafted with pAA were approximately 45-50 degrees; a 50-55 degrees contact angle on pAA-g-SR to be further linked with collagen was subsequently obtained. Moreover, the influence of surface properties toward migration, growth and attachment of CE cells on the modified surfaces was also examined. Here, untreated SR was used as a control. Experimental results indicated that the number of CE cells attached onto the controlled SR was negligible. The attachment of cells onto pAA-grafted surfaces was clearly observed and peusopoda occurred; however, cell growth was depressed. This depression may have been caused by the acid environment of the pAA-grafted membrane. Nevertheless, both cell attachment and growth onto collagen-linked surfaces were significant. In addition, the morphology of the cells attached onto this surface was considered normal for primary cells. Collagen introduced on the SR surface was not denatured, i.e the natural properties of collagen were maintained. The results obtained in this study will hopefully lead to the successful development of modified SR for clinical applications.

Plasma-treated nanostructured TiO(2) surface supporting biomimetic growth of apatite Liu, X., X. Zhao, et al. (2005), Biomaterials 26(31): 6143-50.Abstract: Although some types of TiO(2) powders and gel-derived films can exhibit bioactivity, plasma-sprayed TiO(2) coatings are always bioinert, thereby hampering wider applications in bone implants. We have successfully produced a bioactive nanostructured TiO(2) surface with grain size smaller than 50 nm using nanoparticle plasma spraying followed by hydrogen plasma immersion ion implantation (PIII). The hydrogen PIII nano-TiO(2) coating can induce bone-like apatite formation on its surface after immersion in a simulated body fluid. In contrast, apatite cannot form on either the as-sprayed TiO(2) surfaces (both <50 nm grain size and >50 nm grain size) or hydrogen-implanted TiO(2) with grain size larger than 50 nm. Hence, both a hydrogenated surface that gives rise to negatively charged functional groups on the surface and small grain size (<50 nm) that enhances surface adsorption are crucial to the growth of apatite. Introduction of surface bioactivity to plasma-sprayed TiO(2) coatings, which are generally recognized to have excellent biocompatibility and corrosion resistance as well as high bonding to titanium alloys, makes them more superior than many current biomedical coatings.

Plasma-treated polystyrene surfaces: model surfaces for studying cell-biomaterial interactions van Kooten, T. G., H. T. Spijker, et al. (2004), Biomaterials 25(10): 1735-47.Abstract: Biocompatibility of biomaterials relates, amongst others, to the absence of adverse cellular reactions and modulation of cell adhesion and subsequent responses. With respect to tissue-engineering applications, most materials need to evoke cell adhesion and spreading, while potentially displaying differential cell function. Adhesion has frequently been studied in a controlled fashion, using adhesion-supporting and -inhibiting substrata. The aim of this study is to create a panel of related materials with gradually changing surface characteristics in order to sustain similar individual cell adhesion and spreading, yet different cell population behaviour. A series of polystyrene materials was created with increasing oxygen surface incorporation and, concurrently, decreasing water-contact angles. Individual cells adhered and spread on all surfaces whilst showing well-developed focal adhesions and stress fibres. Cell populations demonstrated a decreased growth on surfaces with lower wettability. The biochemical activity of cell populations was not influenced by the surface treatment, but cell proliferation on surfaces increased with increasing oxygen incorporation. Furthermore, surface coverage with assembled fibronectin matrix was higher on the substrata with higher wettability. Finally, the expression of the adhesion-related proteins cadherin-5, focal adhesion kinase and RhoA was increased on surfaces with higher wettability. Further explorations of the cell biological basis of the observed differential behaviour will give more detailed answers on the rules governing cell-material interactions.

Plasmid delivery in vivo from porous tissue-engineering scaffolds: transgene expression and cellular transfection Jang, J. H., C. B. Rives, et al. (2005), Mol Ther 12(3): 475-83.Abstract: Tissue engineering scaffolds capable of sustained plasmid release can promote gene transfer locally and stimulate new tissue formation. We have investigated the scaffold design parameters that influence the extent and duration of transgene expression and have characterized the distribution of transfected cells. Porous scaffolds with encapsulated plasmid were fabricated from poly(lactide-co-glycolide) with a gas foaming procedure, with wet granulation employed to mix the components homogeneously prior to foaming. Wet granulation enhanced plasmid incorporation relative to standard procedures and also enhanced in vivo transgene expression, possibly through the increased loading and maintenance of the scaffold pore structure. The plasmid loading regulated the quantity and duration of transgene expression, with expression for 105 days achieved at the highest dosage. Expression was localized to the implantation site, though the distribution of transfected cells varied with time. Transfected cells were initially observed at the scaffold periphery (day 3), then within the pores and adjacent to the polymer (day 17), and finally throughout the scaffold interior (day 126). Delivery of a plasmid encoding VEGF increased the blood vessel density relative to control. Correlating scaffold design with gene transfer efficiency and tissue formation will facilitate application of plasmid-releasing scaffolds to multiple tissues.